Pressure treatment of elm posts and cants by Rueping schedules resulted in erratic penetration. Instead of the expected gradual decrease in retention from surface inward in posts, inner zones frequently contained more preservative than the surface quarter inch. Heartwood was found penetrated when sapwood was not. There were numerous skips in treated zones. The prevalence and possible causes were investigated in an effort to find a remedy. The things investigated were effects of: 1) uneven growth rate in the outer zone of posts, 2) growing site, 3) eccentricity and width of growth rings, 4) intermediate wood 5) moisture content, 6) use of initial air pressure or not in treatment, 7) wetwood, 8) tension wood, 9) grain direction of preservative penetration and 10) anatomy of wood. Of these, only intermediate wood, use of initial air, wetwood and wood anatomy seemed to have an effect. The influence of intermediate wood and wetwood is probably minimal but might have some effect.

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